1. Field of the Invention
The present invention relates generally to skeletal plate systems for aligning and maintaining bone portions of the same bone or of different bones in a selected spatial relationship for healing or fusion of the bone portions, respectively. In particular, the present invention relates to skeletal plating systems comprising a plate that is flat and/or convex over a substantial portion of the lower surface of the plate along the longitudinal axis of the plate, bone screws, and locks for locking the bone screws to the plate; to segmentable plates; crossing screw plates; and combination bone screw-lock-plate systems permitting or causing, intersegmental bone compression and/or shortening.
2. Description of the Related Art
It is current practice in orthopedic surgery to use plating systems for joining portions of a broken bone, or for fusion of portions of separate bones. Such systems are composed essentially of plates and screws for aligning and holding the bone portions in a desired position relative to one another. Plating systems have usefulness in the spine, and have general skeletal use on the flat bones, such as the scapula and the pelvis by way of example, and for use on tubular bones, such as the humerus, ulna, radius, femur, and tibia by way of example.
Problems associated with such plating systems have included hardware breakage, hardware loosening, inability to gain adequate fixation, and distraction pseudoarthrosis where the plate will not allow the bone portions to come together over time resulting in a failure to get solid bone healing. These occurrences may cause problems, be associated with surgical failure, and require further surgical procedures to repair the damage, remove the failed hardware, and/or to reattempt skeletal stabilization.
Plates are usually provided to the surgeon for use in sets having a range of sizes so as to provide for such features as biological variability in size, the numbers of segments to be joined, and the length of the portions of bone to be joined. By way of example, it would be common for a plating system for use on the anterior cervical spine and for joining from two to five vertebrae to comprise of from forty to sixty plates. This requires manufacturers to make a large number of different plates, resulting in increased manufacturing costs and inventory costs and increased costs for hospitals to stock large numbers of plates. Further, in the event that a plate is used and another of its kind is needed before it can be replaced, the ability to provide to a patient the best care could be compromised.
Known plating systems additionally experience problems in connection with those procedures where bone grafts are placed between vertebral bodies to achieve an interbody fusion which heals by a process called “creeping substitution”. In this process, dead bone at the interfaces between the graft and the adjacent vertebra is removed by the body, as a prelude to the new growth of bone forming cells and the deposition of new bone. While the plates allow for proper alignment of the vertebrae and their rigid fixation, they can therefore, at the same time unfortunately, hold the vertebrae apart while the resorption phase of the creeping substitution process forms gaps in the bone at the fusion site with the result that the desired fusion does not occur. Such failure in an attempted fusion is known as pseudoarthrosis. A similar phenomenon occurs at the interface of a fractured bone's fragments and is known as non-union. When such a failure occurs, the hardware itself will usually break or become loosened over time requiring further surgery to remove the broken hardware and to again attempt fusion or fracture repair.
Based on a consideration of the features of all of the known plating systems, there remains a need for an improved plating system having the following combination of features:                1) The plate and screws should be sufficiently strong to perform their intended function without mechanical failure;        2) The hardware, and specifically the screws, should be capable of achieving adequate purchase into the bone;        3) Means should be provided for locking each and every bone screw to the plate, and the locking means should be of sufficient size and strength to reliably perform its intended functions;        4) Bone screw locking means should preferably be retainable by the plate prior to bone screw insertion, or should be reliably attachable to a driver to prevent any small parts from becoming loose in the wound;        5) Bone screw orientation should be provided to create maximum screw purchase into bone and high resistance from being dislodged from the bone;        6) An improved and lower cost of production method for the manufacturer of medical plates should be provided;        7) A plate system should be provided for use in various sizes of patients which can be easily made to a selected length by a surgeon to fit the desired application in order to substantially reduce the number of plates required; and        8) Bone screw and plating system should be provided that prevent holding apart of bone portions during the process of creeping substitution and causes, or permits, or both causes and permits the bone portions to move toward each other to permit and promote the fusion or healing of the bone portions.        